Adaptive direct pressure shift control for a motor vehicle transmission

ABSTRACT

An adaptive shift control system for regulating the operation of a fluid operated torque establishing device associated with a specified speed ratio in a motor vehicle automatic transmission. Shifting from a currently engaged speed ratio to the specified speed ratio includes a completion phase during which fluid is supplied to the torque establishing device in accordance with a predetermined pressure schedule to initiate and progressively increase the transmission of torque therethrough. The time required to complete a specified portion of the speed ratio progression is identified and compared to a reference time representative of the time required to complete the progression when the shift quality is not degraded. The predetermined pressure schedule is adjusted based on such comparison so as to adaptively compensate for sources of error which affect the increase of torque transmission through the torque establishing device during the completion phase and cause the shift quality to be degraded.

This invention relates to direct pressure electronic control of a motorvehicle automatic transmission and more particularly to adaptivecorrection of performance deficiencies in the control due tovehicle-to-vehicle variability and wear.

BACKGROUND OF THE INVENTION

Motor vehicle transmissions generally include selectively engageablegear elements for providing two or more forward speed ratios throughwhich engine output torque is applied to the vehicle drive wheels. Inautomatic transmissions, the gear elements which provide the variousspeed ratios are selectively activated through fluid operated torqueestablishing devices, such as clutches and brakes. The brake can be ofthe band or disk type; engineering personnel in the automotive art referto disk type brakes in transmissions as clutches, clutching devices, orreaction clutches. Thus, shifting from one speed ratio to anothergenerally involves releasing (disengaging) the clutching deviceassociated with the current speed ratio and applying (engaging) theclutching device associated with the desired speed ratio. The clutchingdevice to be released is referred to as the off-going clutch, while theclutching device to be applied is referred to as the on-coming clutchingdevice. There is generally a slight overlap between the release andapply, and high quality shifts are only achieved when the release andapply are properly timed and executed.

Conventionally, the control of shifting in an automatic transmission isperformed with hydraulic logic and servo elements responsive to varioussystem parameters such as vehicle speed and throttle position. Fluidpressure signals representative of the various system parameters areprocessed to determine when a shift is in order, and spring elements andfluid orifices within the servo elements determine the timingcalibration for the release and apply of the respective clutchingdevices.

To overcome certain disadvantages of hydraulic control, it has beenproposed to electronically perform at least some of the transmissioncontrol functions. For example, it has been suggested to electronicallydetermine the desired speed ratio based on measured system parameters,and directly control the supply of fluid to the respective clutchingelements to effect shifting from one speed ratio to another. Among theadvantages of electronic control are reduced hardware complexity,increased reliability and greater control flexibility. An example of anelectronic control system for an automatic transmission is given in theU.S. Pat. No. to Marlow 3,688,607 issued Sept. 5, 1972, which patent isassigned to the assignee of the present invention.

The U.S. Pat. No 3,688,607 referred to above discloses a closed loopcontrol where the speed rate of change of a specified transmissionelement is made to conform with a reference rate. The present invention,on the other hand, is directed to an open loop control. In open loopcontrol, the fluid valves are controlled in accordance with apredetermined schedule to effect apply and release of the varioustransmission clutching devices, and the control is not changed in thecourse of a shift in accordance with a measure of a controlledparameter. Such pure open loop control of the clutching devices isacceptable so long as there are no significant variations in the engineand transmission operating characteristics, and no significant assemblytolerances. However, engine and transmission operating characteristicsdo change with time, and the production assembly tolerances may resultin significant vehicle-to-vehicle variability. As a result, controlschedules that produce acceptable ratio shifting in one vehicle mayproduce unacceptable ratio shifting in another vehicle.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide an improvedopen loop direct pressure shift control system, wherein the control isadaptively compensated in the course of its operation for variations inthe operating characteristics of the engine and transmission. In itsbasic form, the control system directs the supply of fluid pressure tothe transmission clutching devices in accordance with empiricallyderived schedules as a function of operator demand and various vehicleparameters. In the course of shifting from one speed ratio to another,certain operating parameters of the transmission are monitored as anindication of the shift quality. If the monitored parameters indicatethat a particular shift did not progress in an optimum manner, thecontroller develops corrections for the empirically derived schedulesinvolved in the shift so that when the shift is repeated at a laterpoint, it will be performed in a more nearly optimum manner.

The present invention addresses the completion phase of ratio shifting.The completion phase follows the fill or preparation phase in which theon-coming clutching device is readied to transmit torque. In thecompletion phase, the transmission of torque through the on-comingclutching device is initiated and progressively increased by supplyingfluid thereto in accordance with a predetermined pressure schedule. Thecompletion phase comprises torque and inertia phases as in conventionalusage, the torque phase being defined as the portion of the completionphase during which there is an exchange of torque between the off-goingand on-coming clutches but no speed change, and the inertia phase beingdefined as the portion of the completion phase during which the speedchange is effected. The predetermined pressure schedules are empiricallyderived to provide optimum shift quality, and may be different for eachclutching device. However, various sources of error affect the pressureof the supplied fluid and the required fluid volume. In this event, thepredetermined pressure schedules are incorrect, and the shift qualitymay be degraded.

Broadly, the adaptive control of this invention adjusts thepredetermined pressure schedules by detecting the time required toeffect the speed change (or a specified portion thereof), comparing thedetected time to a reference time, and developing a correction for thescheduled pressure if necessary. The corrections are developed andapplied in a novel manner designed to maximize the speed of convergencewhile minimizing the converged error.

A co-pending patent application D-9329 is directed to an adaptivecontrol of the fill or preparation phase of the speed ratio shift. Thatcontrol is also described herein.

IN THE DRAWINGS

FIGS. 1a and 1b schematially depict a computer based electronictransmission control system according to the teachings of thisinvention.

FIG. 2 graphically depicts various parameters of the engine andtransmission in the course of a typical upshift.

FIGS. 3-6 graphically depict certain of the parameters shown in FIG. 2for upshifts in which the stored fill time and pressure schedules are inerror.

FIGS. 7-10 graphically depict adaptive compensation of the empiricallydetermined fill time. FIG. 7 depicts the stored fill time (t_(fill)) vs.working pressure ΔP relationship; FIG. 8 depicts typical fill time errordistributions for converged and non-converged systems; FIG. 9 depictsthe scheduling of fill time corrections; and FIG. 10 depicts theapplication of the corrections to the stored t_(fill) vs. ΔPrelationship of FIG. 7.

FIGS. 11-12 graphically depict adaptive compensation of the empiricallydetermined pressure schedules. FIG. 11 depicts the stored pressure ΔPvs. torque variable (T_(v)) vs. time (t) relationship; and FIG. 12depicts the measurement of a predefined inertia phase interval.

FIGS. 13-17 depict flow diagrams representative of suitable programinstructions executed by the computer based controller of FIG. 1 forcarrying out the control functions of this invention. FIG. 13 depicts amain loop program; FIGS. 14-15 depict pressure control algorithms for atypical power-on upshift; FIGS. 16a-16c depict the algorithm foradaptive fill time correction; and FIG. 17 depicts the algorithm foradaptive pressure correction.

Referring now to the drawings, and more particularly to FIGS. 1a and 1b,the reference numeral 10 generally designates a motor vehicle drivetrainincluding an engine 12 and a parallel shaft transmission 14 having areverse speed ratio and four forward speed ratios. Engine 12 includes athrottle mechanism 16 mechanically connected to an operator manipulateddevice such as an accelerator pedal (not shown) for regulating engineoutput torque, such torque being applied to the transmission 14 throughthe engine output shaft 18. The transmission 14 transmits engine outputtorque to a pair of drive axles 20 and 22 through a torque converter 24and one or more of the fluid operated clutching devices 26-34, suchclutching devices being applied or released according to a predeterminedschedule for establishing the desired transmission speed ratio.

Referring now more particularly to the transmission 14, the impeller orinput member 36 of the torque converter 24 is connected to be rotatablydriven by the output shaft 18 of engine 12 through the input shell 38.The turbine or output member 40 of the torque converter 24 is rotatablydriven by the impeller 36 by means of fluid transfer therebetween and isconnected to rotatably drive the shaft 42. A stator member 44 redirectsthe fluid which couples the impeller 36 to the turbine 40, the statorbeing connected through a one-way device 46 to the housing oftransmission 14. The torque converter 24 also includes a clutchingdevice 26 comprising a clutch plate 50 secured to the shaft 42. Theclutch plate 50 has a friction surface 52 formed thereon adaptable to beengaged with the inner surface of the input shell 38 to form a directmechanical drive between the engine output shaft 18 and the transmissionshaft 42. The clutch plate 50 divides the space between input shell 38and the turbine 40 into two fluid chambers: an apply chamber 54 and arelease chamber 56. When the fluid pressure in the apply chamber 54exceeds that in the release chamber 56, the friction surface 52 ofclutch plate 50 is moved into engagement with the input shell 38 asshown in FIG. 1, thereby engaging the clutching device 26 to provide amechanical drive connection in parallel with the torque converter 24. Insuch case, there is no slippage between the impeller 36 and the turbine40. When the fluid pressure in the release chamber 56 exceeds that inthe apply chamber 54, the friction surface 52 of the clutch plate 50 ismoved out of engagement with the input shell 38 thereby uncoupling suchmechanical drive connection and permitting slippage between the impeller36 and the turbine 40. The circled numeral 5 represents a fluidconnection to the apply chamber 54 and the circled numeral 6 representsa fluid connection to the release chamber 56.

A positive displacement hydraulic pump 60 is mechanically driven by theengine output shaft 18 through the input shell 38 and impeller 36 asindicated by the broken line 62. Pump 60 receives hydraulic fluid at lowpressure from the fluid reservoir 64 and supplies pressurized fluid tothe transmission control elements via output line 66. A pressureregulator valve (PRV) 68 is connected to the pump output line 66 andserves to regulate the fluid pressure (hereinafter referred to as linepressure) in line 66 by returning a controlled portion of the fluidtherein to reservoir 64 via the line 70. In addition, pressure regulatorvalve 68 supplies fluid pressure for the torque converter 24 via line74. While the pump and pressure regulator valve designs are not criticalto the present invention, a representative pump is disclosed in the U.S.Pat. No. 4,342,545 to Schuster issued Aug. 3, 1982, and a representativepressure regulator valve is disclosed in the U.S. Pat. 4,283,970 toVukovich issued Aug. 18, 1981 such patents being assigned to theassignee of the present invention.

The transmission shaft 42 and a further transmission shaft 90 each havea plurality of gear elements rotatably supported thereon. The gearelements 80-88 are supported on shaft 42 and the gear elements 92-102are supported on shaft 90. The gear element 88 is rigidly connected tothe shaft 42, and the gear elements 98 and 102 are rigidly connected tothe shaft 90. Gear element 92 is connected to the shaft 90 via afreewheeler or one-way device 93. The gear elements 80, 84, 86 and 88are maintained in meshing engagement with the gear elements 92, 96, 98and 100, respectively, and the gear element 82 is coupled to the gearelement 94 through a reverse idler gear 103. The shaft 90, in turn, iscoupled to the drive axles 20 and 22 through gear elements 102 and 104and a conventional differential gear set (DG) 106.

A dog clutch 108 is splined on the shaft 90 so as to be axially slidablethereon, and serves to rigidly connect the shaft 90 either to the gearelement 96 (as shown) or the gear element 94. A forward speed relationbetween the gear element 84 and shaft 90 is established when dog clutch108 connects the shaft 90 to gear element 96, and a reverse speedrelation between the gear element 82 and shaft 90 is established whenthe dog clutch 108 connects the shaft 90 to the gear element 94.

The clutching devices 28-34 each comprise an input member rigidlyconnected to a transmission shaft 42 or 90, and an output member rigidlyconnected to one or more gear elements such that engagement of aclutching device couples the respective gear element and shaft to effecta driving connection between the shafts 42 and 90. The clutching device28 couples the shaft 42 to the gear element 80; the clutching device 30couples the shaft 42 to the gear elements 82 and 84; the clutchingdevice 32 couples the shaft 90 to the gear element 100; and theclutching device 34 couples the shaft 42 to the gear element 86. Each ofthe clutching devices 28-34 is biased toward a disengaged state by areturn spring (not shown). Engagement of the clutching device iseffected by supplying fluid pressure to an apply chamber thereof. Theresulting torque capacity of the clutching device is a function of theapplied pressure less the return spring pressure, hereinafter referredto as the working pressure ΔP. The circled numeral 1 represents a fluidpassage for supplying pressurized fluid to the apply chamber ofclutching device 28; the circled numeral 2 and letter R represent afluid passage for supplying pressurized fluid to the apply chamber ofthe clutching device 30; the circled numeral 3 represents a fluidpassage for supplying pressurized fluid to the apply chamber of theclutching device 32; and the circled numeral 4 represents a fluidpassage for directing pressurized fluid to the apply chamber of theclutching device 34.

The various gear elements 80-88 and 92-100 are relatively sized suchthat engagement of first, second, third and fourth forward speed ratiosare effected by engaging the clutching devices 28, 30, 32 and 34,respectively, it being understood that the dog clutch 108 must be in theposition depicted in FIG. 1 to obtain a forward speed ratio. A neutralspeed ratio or an effective disconnection of the drive axles 20 and 22from the engine output shaft 18 is effected by maintaining all of theclutching devices 28-34 in a released condition. The speed ratiosdefined by the various gear element pairs are generally characterized bythe ratio of the turbine speed Nt to output speed N_(o). RepresentativeN_(t) /N_(o) ratios for transmission 14 are as follows:

    ______________________________________                                        First - 2.368       Second - 1.273                                            Third - 0.808       Fourth - 0.585                                            Reverse - 1.880                                                               ______________________________________                                    

As indicated above, shifting from a current forward speed ratio to adesired forward speed ratio requires that the clutching deviceassociated with the current speed ratio (off-going) be disengaged andthe clutching device associated with the desired speed ratio (on-coming)be engaged. For example, a shift from the first forward speed ratio tothe second forward speed ratio involves disengagement of the clutchingdevice 28 and engagement of the clutching device 30. As explained below,the timing of such disengagement and engagement is critical to theattainment of high quality shifting, and this invention is directedprimarily to a control system for supplying fluid pressure to thevarious clutching devices 28-34 to achieve consistent high qualityshifting.

The fluid control elements of the transmission 14 include a manual valve140, a directional servo 160 and a plurality of electrically operatedfluid valves 180-190. The manual valve 140 operates in response tooperator demand and serves, in conjunction with directional servo 160,to direct regulated line pressure to the appropriate fluid valves182-188. The fluid valves 182-188, in turn, are individually controlledto direct fluid pressure to the clutching devices 28-34. The fluid valve180 is controlled to direct fluid pressure from the pump output line 66to the pressure regulator valve 68, and the fluid valve 190 iscontrolled to direct fluid pressure from the line 74 to the clutchingdevice 26 of torque converter 24. The directional servo 160 operates inresponse to the condition of the manual valve 140 and serves to properlyposition the dog clutch 108.

The manual valve 140 includes a shaft 142 for receiving axial mechanicalinput from the operator of the motor vehicle in relation to the speedrange the operator desires. The shaft 142 is also connected to anindicator mechanism 144 through a suitable mechanical linkage asindicated generally by the broken line 146. Fluid pressure from the pumpoutput line 66 is applied as an input to the manual valve 140 via theline 148 and the valve outputs include a forward (F) output line 150 forsupplying fluid pressure for engaging forward speed ratios and a reverse(R) output line 152 for supplying fluid pressure for engaging thereverse speed ratio. Thus, when the shaft 142 of manual valve 140 ismoved to the D4, D3, or D2 positions shown on the indicator mechanism144, line pressure from the line 148 is directed to the forward (F)output line 150. When the shaft 142 is in the R position shown on theindicator mechanism 144, line pressure from the line 148 is directed tothe reverse (R) output line 152. When the shaft 142 of manual valve 140is in the N (neutral) or P (park) positions, the input line 148 isisolated, and the forward and reverse output lines 150 and 152 areconnected to an exhaust line 154 which is adapted to return any fluidtherein to the fluid reservoir 64.

The directional servo 160 is a fluid operated device and includes anoutput shaft 162 connected to a shift fork 164 for axially shifting thedog clutch 108 on shaft 90 to selectively enable either forward orreverse speed ratios. The output shaft 162 is connected to a piston 166axially movable within the servo housing 168. The axial position of thepiston 166 within the housing 168 is determined according to the fluidpressures supplied to the chambers 170 and 172. The forward output line150 of manual valve 140 is connected via line 174 to the chamber 170 andthe reverse output line 152 of manual valve 140 is connected via theline 176 to the chamber 172. When the shaft 142 of the manual valve 140is in a forward range position, the fluid pressure in the chamber 170urges piston 166 rightward as viewed in FIG. 1 to engage the dog clutch108 with the gear element 96 for enabling engagement of a forward speedratio. When the shaft 142 of the manual valve 140 is moved to the Rposition, the fluid pressure in chamber 172 urges piston 166 leftward asviewed in FIG. 1 to engage the dog clutch 108 with the gear element 94for enabling engagement of the reverse speed ratio. In each case, itwill be remembered that the actual engagement of the second or reversespeed ratio is not effected until engagement of the clutching device 30.

The directional servo 160 also operates as a fluid valve for enablingthe reverse speed ratio. To this end, the directional servo 160 includesan output line 178 connected to the electrically operated fluid valve186. When the operator selects a forward speed ratio and the piston 166of directional servo 160 is in the position depicted in FIG. 1, thepassage between lines 176 and 178 is cut off; when the operator selectsthe reverse gear ratio, the passage between the lines 176 and 178 isopen.

The electrically operated fluid valves 180-190 each receive fluidpressure at an input passage thereof from the pump 60, and areindividually controlled to direct fluid pressure to the pressureregulator valve 68 or respective clutching devices 26-34. The fluidvalve 180 receives line pressure directly from pump output line 66, andis controlled to direct a variable amount of such pressure to thepressure regulator valve 68 as indicated by the circled letter V. Thefluid valves 182, 186 and 188 receive fluid pressure from the forwardoutput line 150 of manual valve 140, and are controlled to directvariable amounts of such pressure to the clutching devices 34, 32 and 28as indicated by the circled numerals 4, 3 and 1, respectively. The fluidvalve 186 receives fluid pressure from the forward output line 150 andthe directional servo output line 178, and is controlled to direct avariable amount of such pressure to the clutching device 30 as indicatedby the circled numeral 2 and the circled letter R. The fluid valve 190receives fluid pressure from line 74 of pressure regulator valve 68, andis controlled to direct a variable amount of such pressure to therelease chamber 56 of the clutching device 26 as indicated by thecircled numeral 6. The apply chamber 54 of the clutching device 26 issupplied with fluid pressure from the output line 74 via the orifice 192as indicated by the circled numeral 5.

Each of the fluid valves 180-190 includes a spool element 210-220,axially movable within the respective valve body for directing fluidflow between input and output passages. When a respective spool element210-220 is in the rightmost position as viewed in FIG. 1, the input andoutput passages are connected. Each of the fluid valves 180-190 includesan exhaust passage as indicated by the circled letters EX, such passageserving to drain fluid from the respective clutching device when thespool element is shifted to the leftmost position as viewed in FIG. 1.In FIG. 1, the spool elements 210 and 212 of fluid valves 180 and 182are shown in the rightmost position connecting the respective input andoutput lines, while the spool elements 214, 216, 218 and 220 of thefluid valves 184, 186, 188 and 190 are shown in the leftmost positionconnecting the respective output and exhaust lines. Each of the fluidvalves 180-190 includes a solenoid 222-232 for controlling the positionof its spool element 210-220. Each such solenoid 222-232 comprises aplunger 234-244 connected to the respective spool element 210-220 and asolenoid coil 246-256 surrounding the respective plunger. One terminalof each such solenoid coil 246-256 is connected to ground potential asshown, and the other terminal is connected to an output line 258-268 ofa control unit 270 which governs the solenoid coil energization. As setforth hereinafter, the control unit 270 pulse-width-modulates thesolenoid coils 246-256 according to a predetermined control algorithm toregulate the fluid pressure supplied to the pressure regulator 68 andthe clutching devices 26-34, the duty cycle of such modulation beingdetermined in relation to the desired magnitude of the suppliedpressures.

While the fluid valves 180-190 have been illustrated as spool valves,other types of valves could be substituted therefor. By way of example,valves of the ball and seat type could be used. In general terms, thefluid valves 180-190 may be mechanized with any three-portpulse-width-modulated valving arrangement.

Input signals for the control unit 270 are provided on the input lines272-284. A position sensor (S) 286 responsive to movement of the manualvalve shaft 142 provides an input signal to the control unit 270 vialine 272. Speed transducers 288, 290 and 292 sense the rotationalvelocity of various rotary members within the transmission 14 and supplyspeed signals in accordance therewith to the control unit 270 via lines274, 276, and 278, respectively. The speed transducer 288 senses thevelocity of the transmission shaft 42 and therefore the turbine ortransmission input speed N_(t) ; the speed transducer 290 senses thevelocity of the drive axle 22 and therefore the transmission outputspeed N_(o) ; and the speed transducer 292 senses the velocity of theengine output shaft 18 and therefore the engine speed N_(e). Theposition transducer 294 is responsive to the position of the enginethrottle 16 and provides an electrical signal in accordance therewith tocontrol unit 270 via line 280. A pressure transducer 296 senses themanifold absolute pressure (MAP) of the engine 12 and provides anelectrical signal to the control unit 270 in accordance therewith vialine 282. A temperature sensor 298 senses the temperature of the oil inthe transmission fluid reservoir 64 and provides an electrical signal inaccordance therewith to control unit 270 via line 284.

The control unit 270 responds to the input signals on input lines272-284 according to a predetermined control algorithm as set forthherein, for controlling the energization of the fluid valve solenoidcoils 246-256 via output lines 258-268. As such, the control unit 270includes an input/output (I/O) device 300 for receiving the inputsignals and outputting the various pulse-width-modulation signals, and amicrocomputer 302 which communicates with the I/O device 300 via anaddress-and-control bus 304 and a bidirectional data bus 306. Flowdiagrams representing suitable program instructions for developing thepulse-width-modulation outputs in accordance with the teachings of thisinvention are depicted in FIGS. 13-17.

As indicated above, every shift from one speed ratio to another involvesdisengagement of an off-going clutching device and engagement of anon-coming clutching device. Each shift includes a fill phase duringwhich the apply chamber of the on-coming clutch is filled with fluid, atorque phase during which the torque capacity of the off-going clutchingdevice is reduced and the torque capacity of the on-coming clutchingdevice is increased, and an inertia phase during which the turbine isaccelerated to a new velocity determined according to the new speedratio. Such phases are defined in terms of times t₀ -t₄ for a typical2-3 upshift in graphs A-D of FIG. 2, each of the graphs having a commontime base. Graph A depicts the turbine speed N_(t) ; Graph B depicts thepressure command for the on-coming clutching device fluid valve; Graph Cdepicts the engine torque T_(e) and the torque carried by the clutchingdevices 30 and 32; and Graph D depicts the transmission output torqueT_(o).

Prior to the shift activity, the relation between the turbine and outputspeeds N_(t) and N_(o) is static and determined according to the secondspeed ratio. In addition, the output torque T_(o) is substantiallyconstant. In the course of the shift, the speed and torque relationshipsbecome dynamic as the engine torque T_(e) is shifted from the clutchingdevice 30 to the clutching device 32. Following the shift activity, theoutput torque is once again substantially constant, and the relationbetween N_(t) and N_(o) is determined according to the third speedratio.

At time t₀ when it is determined that a 2-3 ratio shift is desired, thesolenoid coil 250 of fluid valve 184 is energized at a duty cycle of100% to commence filling the apply chamber of clutching device 32. Thismarks the beginning of the fill phase of the shift, as indicated belowGraph D. Although not shown in FIG. 2, the solenoid coil 252 of fluidvalve 186 is energized at a relatively high duty cycle during the fillphase to maintain engagement of the second speed ratio. At time t₁,t_(fill) seconds after time t₀, the fluid pressure in the apply chamberof clutching device 32 is sufficiently great to compress the clutchreturn spring, marking the end of the fill phase and the beginning ofthe torque phase, as indicated below Graph D. Thereafter, the pressurecommand is reduced to a value corresponding to an empirically derivedinitial pressure P_(x) and progressively increased to a valuecorresponding to an empirically derived final pressure P_(y). Duringsuch time, the torque T_(cd32) carried by the on-coming clutching device32 progressively increases and the torque T_(cd30) carried by theoff-going clutching device 30 progressively decreases, as seen in GraphC. The output torque T_(o) in this interval is determined according tothe sum of T_(cd30) and T_(cd32) as reflected through the respectivespeed ratios of transmission 14, and progressively decreases as seen inGraph D. At time t₂, the torque T_(cd32) equals the engine torque T_(e),the torque T_(cd30) is reduced to zero, and the output torque T_(o)begins to rise with T_(cd32) as seen in Graphs C-D. After time t₂, thetorque T_(cd32) continues to rise and the torque differential between itand the engine torque T_(e) urges the turbine to decelerate toward thethird ratio speed, designated by the trace 308 in Graph A. At time t₃,the turbine speed N_(t) begins to decrease, marking the end of thetorque phase and the beginning of the inertia phase as indicated belowGraph D. As the turbine speed N_(t) decreases, the engine torque T_(e)increases, as seen in Graph C. At time t₄, the turbine speed joins thethird speed trace 308, marking the end of the inertia phase and theshift as indicated below Graph D. Since the clutching device 32 is nolonger slipping at such point, the torque T_(cd32) drops to the level ofthe engine torque T_(e), and the output torque T_(o) drops to thepost-shift level. The shaded area 309 between the T_(e) and T_(cd32)traces in Graph C is referred to as the inertia torque and representsthe amount of torque the on-coming clutching device must exert to effectthe speed change.

The on-coming clutch fill time and the clutch pressure schedules areindividually determined for each ratio shift. If both are correct, andthe various control elements each function as expected, the ratio shiftwill progress in the desired manner as depicted in FIG. 2, with neitherexcessive harshness nor excessive slippage of the friction devices.These are the essential ingredients of open loop ratio shifting. Asindicated above, however, a certain amount of variation in the engineand transmission operating characteristics can be expected over the lifeof the vehicle due to wear. Moreover, there may be somevehicle-to-vehicle variability due to assembly and component tolerances.If the on-coming clutching device begins developing torque capacityeither before or after the end of the calculated fill time, the exchangeof torque capacity between the off-going and on-coming clutching deviceswill not proceed according to schedule. In this regard, the consequencesof overfill and underfill errors are graphically illustrated in FIGS. 3and 4. Similarly, the shift quality is degraded if the clutch pressureduring the torque and inertia phases is too high or too low for a givenoperating condition. The consequences of improperly low and highpressure scheduling are graphically illustrated in FIGS. 5 and 6.

FIGS. 3-6 each include Graphs A, B, and C corresponding to the Graphs A,C, and D of FIG. 2. To facilitate comparison of the various traces withthe corresponding traces of FIG. 2, each of the graphs of FIGS. 3-6includes the time scale designations t₀ -t₄ as defined in reference tothe normal high quality shift of FIG. 2. In addition, the static torqueand speed levels shown in FIG. 2 have been adopted in FIGS. 3-6.

When the stored fill time t_(fill) is too high--FIG. 3--the on-comingclutching device 32 is overfilled, and begins transmitting torque priorto time t₁, as seen by the T_(cd32) trace in Graph B. In such case, thecapacity T_(cd32) of the on-coming clutching device reaches the enginetorque T_(e) before the capacity T_(cd30) of the off-going clutchingdevice is reduced to zero as seen at time t_(x) in Graph B. As a result,the on-coming clutching device 32 is opposed by the off-going clutchingdevice 30, resulting in what is known as bind-up, which bind-up reducesthe output torque T_(o) as compared to the shift of FIG. 2. Themagnitude of the output torque reduction is graphically represented bythe shaded area 310 of Graph C. The bind-up also results in a momentaryunwinding of the various transmission and driveline shafts, as evidencedby the momentary reduction 311 in turbine speed N_(t).

When the stored fill time t_(fill) is too low--FIG. 4--the on-comingclutching device 32 is underfilled, and does not begin transmittingtorque until after time t₁, as seen by the T_(cd32) trace in Graph B. Insuch case, the output torque is reduced as compared to the shiftdepicted in FIG. 2, the amount of such reduction being graphicallyrepresented by the shaded area 312 in Graph C. Moreover, the torquecapacity C_(cd32) of the on-coming clutching device is not yetsufficient to transmit all of the engine torque T_(e) when the off-goingclutching device is completely released at time t₂. This causes aturbine speed flare, as indicated by the reference numeral 313 in GraphA.

When the scheduled pressure for the on-coming clutching device is toolow--FIG. 5--the torque capacity C_(cd32) is reduced as compared to FIG.2. As a result, the duration of the inertia phase becomes excessivelylong, degrading the shift quality and inducing excessive wear andheating of the clutching devices. For the example depicted in FIG. 5,the length of the inertia phase is designated by the interval 314.

When the scheduled pressure for the on-coming clutching device is toohigh--FIG. 6--the torque capacity C_(cd32) is increased as compared toFIG. 2, and the turbine is rapidly decelerated to its new speed as seenin Graph A. As a result, the duration of the inertia phase is relativelyshort, as designated by the interval 316. In addition, the rapid turbinedeceleration causes a transient increase in the output torque To asindicated by the shaded area 318 in Graph C, and produces an undesirablyharsh shift.

According to this invention, the empirically derived fill times andpressure schedules for the various clutching devices are adaptivelycompensated in the course of vehicle operation so as to achieveconsistent high quality ratio shifting. In each case, specifiedoperating parameters are monitored during each upshift, and thencompared to reference parameters to determine if the shift progressed ina desired manner. If the comparison of the monitored and referenceparameters indicates that the shift did not progress in the desiredmanner, the respective fill time and/or pressure schedule is adjusted ina corrective direction so that subsequent shifting will be carried outin a more nearly optimum manner.

The empirically derived fill times are adaptively corrected bymonitoring the time interval between the start of fill and the turndownor reduction in turbine speed during each upshift. Since the turbinespeed turndown marks the beginning of the inertia phase of the shift,such interval is referred to herein as the inertia phase delay, IPDELAY.The measured IPDELAY is compared to a reference desired delay, DESDELAY,to determine if the on-coming clutching device was properly filled attime t₁. If the stored fill time t_(fill) is correct, the on-comingclutching device will be properly filled at time t₁, and IPDELAY will besubstantially equal to DESDELAY. If the stored fill time t_(fill) is tooshort and the on-coming clutching device is underfilled at time t₁, theturbine speed turndown will be late as shown in FIG. 3, and IPDELAY willbe significantly greater than DESDELAY. In this event, the control unit270 operates to increase the fill time t_(fill) for the respectiveclutching device so that subsequent shifts involving that clutchingdevice will be performed in a more nearly optimum manner. If the storedfill time t_(fill) is too long and the on-coming clutching device isoverfilled (already developing torque capacity) at time t₁, theresulting bind-up and momentary turbine speed reduction described inreference to FIG. 4 will be sensed as an early turbine speed turndown,and IPDELAY will be significantly less than DESDELAY. In this event, thecontrol unit 270 operates to decrease the fill time t_(fill) for therespective clutching device so that subsequent shifts involving thatclutching device will be carried out in a more nearly optimum manner.

In practice, the turbine speed flare characteristic associated withunderfill is more easily identified than the momentary reductionassociated with overfill. This is especially true in low torque, highturbine speed shifts since the momentary turbine speed changesassociated with overfill are but a small percentage of the steady stateturbine speed. This difficulty is overcome according to this inventionby periodically decrementing the fill time while the vehicle is beingoperated under conditions for which overfills cannot be accuratelyidentified. When the incremental changes in fill time result in adetectable underfill, the control unit 270 operates as described aboveto increase the fill time. In this way, the stored fill times for thevarious clutching devices are maintained relatively close to the correctvalues even during periods of vehicle operation for which overfilldetection may not be reliable. In addition, large overfill errorindications are treated as small overfill indications until several(three, for example) such error indications are successively sensed.

The description of the mechanisms for identifying turndown of turbinespeed and for adaptively compensating the clutching device fill times inresponse thereto is prefaced by a description of the mechanism forcomputing the fill time. As briefly set forth above, the fill time for agiven clutching device is determined primarily as a function of therequested line pressure, the geometry of the clutching device, and theviscosity of the fluid. Algebraically, the fill time t_(fill) is givenas follows:

    t.sub.fill =V/ [A* (2ΔP/r).sup.1/2]

where V is the volume of the apply chamber, A is the area of the clutchpiston, ΔP is the apply pressure less the return spring pressure, and ris the fluid viscosity. To improve the fill time calculation efficiency,this invention defines a fill time vs. pressure (ΔP) function lookuptable as graphically depicted by the trace 320 of FIG. 7. The trace 320takes into account the clutching device geometry and is in the form ofan inverse square root function due to the ΔP dependence as set forth inthe algebraic expression above. Rather than store the entire function,just the two fill time points (designated L and H) corresponding to thelowest and highest available line pressures ΔP_(L) and ΔP_(H) are storedby control unit 270. The fill time is linearly interpolated along thebroken line 322 connecting the fill time points L and H, and thenmathematically adjusted to reflect the inverse square root form (1/√ΔP)of the trace 320. The adjusted fill time is then modified by an oiltemperature dependent factor to compensate for variations in the fluidviscosity.

The time required to effect a turndown in turbine speed in the course ofan upshift is determined by starting a timer at the end of fill andstopping the timer upon detection of the turndown. The timed intervalmay thus be viewed as the delay between the end of fill and thebeginning of the inertia phase. The turndown is identified by predictinga future turbine speed (through an extrapolation process) and comparingthe actual turbine speed with the predicted turbine speed. Turbine speedis detected in terms of T/TP, the time between pulses received from theturbine speed transducer 288 of FIG. 1. By nature of its definition,T/TP varies inversely with turbine speed. The measured values of T/TPare averaged by a first order lag function to determine the average timebetween turbine pulses, AT/TP. In turn, the difference (AT/TP-T/TP) iscomputed and subjected to a first order lag function to determine theaverage change in time between turbine pulses, AΔT/TP. Algebraically,the predicted time between turbine pulses for a point (k+2) seconds inthe future, PT/TP(k+2), is given by the expression:

    PT/TP (k+2AT/TP(k)-[AT/TP(k-4)-AT/TP(k)]/2-[AΔT/TP(k-4)+AΔT/TP(k)[

The term k represents several loop times of control unit 270, and thepredicted time between turbine pulses one loop time (L) in the future,PT/TP(L), is determined by linear interpolation between the calculatedvalues. The error time between turbine pulses ET/TP--i.e., thedifference between actual and predicted time between turbine pulsesT/TP(L) PT/TP(L)--is computed to identify the turndown of turbine speed.Due to the inverse relation between turbine speed and time T, theturndown is identified as a significant error ET/TP of positive sign.

Several steps are taken to minimize the likelihood of false turndowndetection. The main concern in this regard is that noise or fluctuationof the turbine speed signal (due to bumps in the road surface, forexample) causes some difference between the predicted and actual timebetween turbine pulses. Primarily, the likelihood of false detection isminimized by the employment of novel signal processing techniques,including (1) enabling the detection algorithm only in a specified timewindow during the shift, (2) defining a two-stage error threshold foridentifying the turndown, and (3) adjusting the two-stage errorthreshold in accordance with a measure of the turbine speed signalnoise. The time window during which the detection algorithm is enabledis defined so that the algorithm is operative to detect the occurrenceof turbine speed turndown in worst case overfill and underfillsituations. The two-stage error threshold comprises a first relativelylow threshold and a second relatively high threshold. When the firstthreshold is exceeded, the fill timer is sampled. If the secondthreshold is subsequently exceeded, the occurrence of turndown isconfirmed, and turndown indication is given. If the second threshold isnot subsequently exceeded, the error is assumed to be noise induced, andthe fill timer is permitted to continue counting. In this way, noiseinduced error is distinguished from turndown induced error. The measureof the turbine speed noise for adjusting the first and second thresholdsis obtained by applying a first order lag function to the error signalET/TP, such filtered signal being identified herein as FET/TP. Thethresholds are increased with increasing FET/TP, and decreased withdecreasing FET/TP.

In spite of the above signal processing techniques, it is possible thatturbine speed noise could cause consecutive significant error signals,and trigger an early turndown indication. The consequence of such afalse indication is mitigated (as explained below) by limiting theadaptive correction to a relatively small value until severalconsecutive overfills have been indicated. In the illustratedembodiment, three consecutive overfill indications are required before alarge fill time correction can be issued.

The adaptive compensation mechanism interfaces with the above describedfill time determination technique by suitably modifying the fill timeendpoints L and H. The amount by which the endpoints L and H aremodified is determined in relation to the fill time error (E_(ft))between the detected and expected times to turbine speed downturn. Theexpected time to turndown is empirically determined in relation to thetype of shift and either the working pressure ΔP or the input torqueT_(i). As an example, let it be assumed that the torque phase of a givenupshift is expected to take 30 ms. If the actual turbine speed turndownis detected 30 ms after the end of the calculated fill time (E_(ft) =0ms), it is assumed that the calculated fill time is correct and noadaptive compensation is attempted. However, if the turndown is detected60 ms after the end of the calculated fill time (E_(ft) =+30 ms), it isassumed that the calculated fill time is too short--that is, theon-coming clutching device was underfilled and developed torque capacitytoo late. On the other hand, if the turndown is detected 10 ms after theend of the calculated fill time (E_(ft) =+-20 ms), it is assumed thatthe calculated fill time is too long--that is, the on-coming clutchingdevice was overfilled and developed torque capacity too early. The signof the error indicates whether the on-coming clutching device wasunderfilled or overfilled, and the magnitude indicates the amount oferror.

The fill time error E_(ft) as defined above is used to determine a filltime correction (C_(ft)) for adaptively compensating the stored filltime endpoints L and H as defined in FIG. 7. The fill time correctionamount is determined in accordance with a gain scheduling techniquedesigned to achieve fast convergence of the calculated fill times withminimum converged misadjustment. Functionally, the intent is to providelarge adjustment when large errors of a given sign are sensed, andlittle or no adjustment when a distribution of errors are sensed.

The randomness of the system operation is graphically depicted in FIG.8, where traces 330 and 332 represent typical distributions of sensedfill time error for a clutching device. The distribution trace 330 iscentered around zero error, and therefore represents a system which isaccurately calibrated and which cannot be improved by adaptivecompensation. The shape of the trace is influenced by the controlalgorithms of control unit 270 and the physical control elements oftransmission 14. Presumably, such algorithms and elements are designedto provide a sufficiently high level of repeatability so that acceptableshift quality is achieved within most, if not all of the distributionrange. That is, for the example depicted in FIG. 8, a fill time error ofplus or minus e₁ would not result in unacceptable shift quality. Thedistribution trace 332 is centered around an error value e₂, andtherefore represents a system which is not accurately calibrated andwhich could be improved by adaptive compensation. Nearly all of the filltime errors within the randomness of the distribution trace 332 aregreater than e₁, and would likely result in unacceptable shift quality.

The aim of adaptive compensation is to move the distribution trace 332to the left as viewed in FIG. 8 by the amount of e₂ so as to achieve theshift quality associated with the distribution trace 330. However, thecontrol unit 270 cannot determine the center of the error distributionbased on a given error measurement. For example, a measured error of e₁could occur with a system represented by the distribution trace 330, asystem represented by the distribution trace 332, or a systemrepresented by any distribution trace therebetween. If the distributiontrace 332 is representative of the system, a relatively large adaptivemodification of the fill time would be proper. If the distribution trace330 is representative of the system, an adaptive modification of thefill time would be a misadjustment.

The difficulty set forth above is overcome according to this inventionby establishing a nonlinear base gain schedule which is relatively lowfor achieving relatively low converged misadjustment and a nonlineardirection sensitive dynamic gain modifier for increasing the baseschedule gain in relation to the time integral of the measured error.The authority of the dynamic gain modifier is limited by a maximumoverall gain which is dependent on the error magnitude, and the modifieris reset to zero when a significant error of the opposite sign isdetected. In FIG. 9, the base gain schedule and the maximum overall gainare graphically depicted as a function fill time error E_(ft). The basegain schedule is depicted by the trace 334 and the maximum overall gainis depicted by the trace 336. As indicated above, fill time error thatis positive in sign (underfill) produces a positive correction forincreasing the fill time endpoints; fill time error that is negative insign (overfill) produces a negative correction for decreasing the filltime endpoints. The dynamic gain modifier can increase the base gaincorrection (in either positive or negative sense) up to the maximumoverall gain in relation to the integral of error signals in onedirection. Graphically, the shaded areas between the traces 334 and 336represent the authority range of the dynamic gain modifier. In this way,the fill time correction is determined primarily in accordance with thebase schedule gain when the error distribution is centered at or nearzero error. When the error distribution becomes significantly skewed ineither direction, the dynamic gain modifier becomes active and adds tothe base gain to achieve fast correction of the error. Essentially, theadaptive corrections become greater with increased detected error andincreased time required to correct the error.

The fill time correction C_(ft) is apportioned between the fill timeendpoints L and H in accordance with the fluid pressure applied to theon-coming clutching device during the upshift. The mechanization of suchapportionment is graphically depicted in FIG. 10, where the trace 340represents a gain factor G_(L) for the endpoint L, and the trace 342represents a gain factor G_(H) for the endpoint H. After any upshiftwhere a fill time correction C_(ft) is in order, the endpoint L isadjusted by the amount (C_(ft) *G_(L)), and the endpoint H is adjustedby the amount (C_(ft) *G_(H)). In future shifts involving the subjectclutching device, the calculated fill time t_(fill) will more correctlyreflect the actual time required to fill its apply chamber and strokethe return spring to develop torque capacity. As a result, changingconditions which affect the fill time of the clutching device are fullycompensated for over a number of upshifts involving the clutchingdevice.

The empirically derived pressure schedules for the on-coming clutchingdevices are adaptively corrected by monitoring the inertia phaseinterval t_(ip) during each upshift and comparing such interval to areference interval t_(rip). If the stored pressure schedule is correct,the shift will progress in a desired manner, and t_(ip) will besubstantially equal to t_(rip). If the stored pressure schedule is toohigh, the shift will be too harsh, and t_(ip) will be significantly lessthan t_(rip). In such event the control unit 270 will operate todecrease the stored pressure schedule so that subsequent shiftsinvolving that clutching device will be carried out in a more nearlyoptimum manner. If the stored pressure schedule is too low, the shiftwill take too long, and t_(ip) will be significantly greater thant_(rip). In such event, the control unit 270 will operate to increasethe stored pressure schedule.

In operation, the pressure schedules are determined as a function of atorque variable T_(v). The torque variable T_(v), in turn, is determinedas a function of the gear set input torque T_(i) and the entry turbinespeed N_(te), N_(te) being defined as the turbine speed N_(t) at the endof the fill phase. The entry turbine speed, in combination withpredicted turbine speed for the new speed ratio, provides an indicationof the inertia torque required to effect the shift. With thisinformation, the clutch pressures are scheduled so that the timerequired to effect the shift varies in direct relation to ΔN_(t), forany value of input torque T_(i). However, some input torque dependencymay be introduced if it is desired to stretch-out or soften off-patternshifts, such as high speed-low torque upshifts.

The status of the torque converter clutching device 26 also affects thescheduled pressure. If the clutching device 26 is disengaged during theshift, the torque converter 24 effectively isolates the inertia of theengine 12, and the on-coming clutching device must only overcome theturbine inertia. If the clutching device 26 is engaged during the shift,the inertia torque must be significantly greater since both the engineand turbine inertias must be overcome.

In mechanizing the determination of T_(v), the gear set input torqueT_(i) is calculated as a function of the engine manifold absolutepressure (MAP), the engine pumping efficiency (K), a mechanical frictionterm (T_(f)), the accessory load torque (T_(L)), and the torquemultiplication ratio (T_(c)) of the torque converter 24 according to thefollowing expression:

Ti T_(i) =[(MAP×K)-T_(f) -T_(L) ]×T_(c)

The engine MAP is determined from the sensor 296, while the efficiency Kis stored based on previously determined data. The mechanical frictionterm T_(f) is determined as a function of engine speed, and the loadtorque term T_(L) is determined by loading indicators. The torquemultiplication ratio T_(c) is determined as a function of the speedratio N_(t) /N_(e).

The desired pressures for the on-coming and off-going clutching devicesare stored as a function of the torque variable T_(v) and time, asgraphically depicted in FIG. 11. For any given value of torque variableT_(v), the ΔP vs. time schedule is defined by a pair of pressureendpoints, one such endpoint corresponding to an initial time t_(i), andthe other corresponding to a final time t_(f). The time t_(i) marks thebeginning of the torque phase, and the time t_(f) marks the end of theinertia phase. If the calculated torque variable T_(v) is zero ornear-zero, for example, the ΔP vs. time schedule is defined by the line350 connecting the pressure endpoints P_(a) and P_(b). If the calculatedtorque variable T_(v) is very high, as designated by T_(v) (max), the ΔPvs. time schedule is defined by the line 352 connecting the pressureendpoints P_(c) and P_(d). In practice, only the four pressure endpointsP_(a), P_(b), P_(c), and P_(d) need be stored by the control unit 270.For any calculated torque variable value T_(v1) between zero and T_(v)(max), the initial pressure P_(x) is linearly interpolated along theline 354 connecting the initial pressure endpoints P_(a) and P_(c), andthe final pressure P_(y) linearly interpolated along the line 356connecting the final pressure endpoints P.sub. and P_(d). In such case,the ΔP vs. time schedule for the shift would be defined by the line 358connecting the initial and final pressures P_(x) and P_(y). The time(t_(f) -t_(i)) for a given shift is empirically derived and stored inthe memory of control unit 270. It should be understood, of course thatthe pressure schedules may be defined by three or more pressureendpoints if desired using the techniques described herein.

Although the pressure control algorithm set forth above provides goodresults in a well calibrated system, it is recognized herein thatadaptive compensation is needed to correct for variations in systemperformance which affect the inertia phase torque. According to thisinvention, the pressure schedule of FIG. 11 is adaptively compensated bydeveloping a reference inertia phase interval t_(rip) and comparing itto a measure of the actual inertia phase interval t_(ip). If thecomparison indicates that t_(ip) is too long, the pressure schedule iscorrected upward; if the comparison indicates that t_(ip) is too short,the pressure schedule is corrected downward. If the scheduled clutchpressures are developed to result in constant shift time for a givenentry turbine speed N_(et) as described above, the reference intervalt_(rip) is determined solely in relation to the entry turbine speedN_(te). If some input torque dependency is included to soften theoff-pattern shifts as mentioned above, the reference interval t_(rip) isdetermined as function of both T_(i) and N_(te).

The actual inertia phase interval t_(ip) is determined in the course ofeach upshift by monitoring the speed ratio N_(t) /N_(o). The initial andfinal ratios are known, and the control unit 270 continuously computesthe percent of ratio completion, % RAT. Algebraically, $RAT is given bythe expression:

    % RAT=|RAT.sub.meas -RAT.sub.old |/|Rat.sub.new -RAT.sub.old |

where RAT_(meas) is the actual ratio, RAT_(old) is the ratio of thepreviously engaged speed ratio, and RAT_(new) is the ratio of thedesired speed ratio. The speed ratio for a typical 2-3 ratio shift isgraphically represented by the trace 360 of FIG. 12. In such example,the ratio changes from the second speed ratio value of 1.273 RPM/RPM tothe third speed ratio value of 0.808 RPM/RPM. Technically, the inertiaphase of the shift begins at time t₀ when the turbine speed (and hence,the ratio) begins to change, and ends at time t₃ when the ratio reachesthe third speed ratio value of 0.808 RPM/RPM. However, the initial andfinal nonlinearity of the trace makes measurement of the interval t₀ -t₃somewhat difficult. To obtain a more repeatable indication of theinertia phase interval t_(ip) and to permit reliable extrapolation ofthe available data, t_(ip) is defined as the interval between 20% and80% of ratio completion. In the example of FIG. 12, the ratio change is20% complete (1.180 RPM/RPM) at time t₁ and 80% complete (0.901 RPM/RPM)at time t₂.

When a significant difference between the measured inertia phaseinterval t_(ip) and the reference inertia phase interval t_(rip) isdetected, the control unit 270 develops a pressure correction amountC_(p) as a function of such difference and apportions the correctionamount C_(p) among the four stored pressure endpoints P_(a), P_(b),P_(c), and P_(d) defined in FIG. 11. The pressure correction amountC_(p) is determined in a manner similar to that described above inreference to the fill time correction amount C_(ft). That is, anonlinear base gain schedule and direction sensitive dynamic gainmodifier similar to that as described above in reference to FIG. 9 isused.

The pressure correction amount C_(p) is apportioned among the storedpressure endpoints P_(a), P_(b), P_(c), and P_(d) as a function of thetorque variable T_(v) used to schedule the shift. One portion of thecorrection amount C_(p) is applied equally to the endpoints P_(a) andP_(b), and the remaining portion is applied equally to the endpointsP_(c) and P_(d). The apportionment is performed in a manner similar tothat of the fill time correction amount C_(ft) (described above inreference to FIG. 10) by developing a gain term G_(L) for the endpointsP_(a) and P_(b), and a gain term G_(H) for the endpoints P_(c) andP_(d). The endpoints P_(a) and P_(b) are adjusted by the amount (C_(p)*G_(L)), and the endpoints P_(c) and P_(d) are adjusted by the amount(C_(p) *G_(H)) When the torque variable T_(v) is relatively low, most ofthe correction amount C_(p) will be applied to the endpoints P_(a) andP_(b). When the torque variable T_(v) is relatively high, most of thecorrection amount C_(p) will be applied to the endpoints P_(c) andP_(d). Due to the adaptive correction, changing conditions which affectthe inertia phase interval are compensated for after a number of suchupshifts.

The flow diagrams depicted in FIGS. 13-17 represent program instructionsto be executed by the microcomputer 302 of control unit 270 inmechanizing ratio shifting and the adaptive control functions of thisinvention. The flow diagram of FIG. 13 represents a main or executiveprogram which calls various subroutines for executing particular controlfunctions as necessary. The flow diagrams of FIGS. 14-17 represent thefunctions performed by those subroutines which are pertinent to thepresent invention.

Referring now more particularly to FIG. 13, the reference numeral 370designates a set of program instructions executed at the initiation ofeach period of vehicle operation for initializing the various registers,timers, etc. used in carrying out the control functions of thisinvention. Following such initialization, the instruction blocks 372-384are repeatedly executed in sequence as designated by the flow diagramlines connecting such instruction blocks and the return line 386.Instruction block 372 reads and conditions the various input signalsapplied to I/O device 300 via the lines 272-284, and updates(increments) the various control unit timers. Instruction block 374calculates various terms used in the control algorithms, including theinput torque T_(i), the torque variable T_(v), and the speed ratio N_(o)/N_(i). The algebraic expressions used to calculate the terms T_(i) andT_(v) are given above in reference to FIG. 11. Instruction block 376determines the desired speed ratio, R_(des), in accordance with a numberof inputs including throttle position, vehicle speed, and manual valveposition. In transmission control, this function is generally referredto as shift pattern generation. Instruction block 378 determines theclutching device pressure commands for effecting a ratio shift, ifrequired. The pressure commands for the pressure regulator valve PRV andnon-shifting clutching devices are also determined. An expandeddescription of the instruction block 378 is set forth below in referenceto the flow diagrams of FIGS. 14-15. Instruction block 380 converts theclutching device and PRV pressure commands to a PWM duty cycle based onthe operating characteristics of the various actuators (empiricallydetermined), and energizes the actuator coils accordingly. Instructionblock 382 relates to the determination of adaptive corrections for theempirically derived clutch pressure schedules, and is discussed in moredetail below in reference to FIG. 17. Instruction block 384 relates tothe determination of adaptive corrections for the empirically derivedclutch fill times, and is discussed in more detail below in reference toFIGS. 16a- 16c.

As indicated above, the flow diagrams of FIGS. 14 and 15 set forth theclutch and PRV pressure determination algorithm generally referred to atthe main loop instruction block 378 of FIG. 13. On entering suchalgorithm, the blocks designated generally by the reference numeral 388are executed to set up initial conditions if a shift is in order. If ashift is in order, the blocks designated generally by the referencenumeral 390 are executed to develop pressure commands for the clutchingdevices involved in the shift. Thereafter, the instruction blocks 392and 394 are executed to develop pressure commands for the non-shiftingclutches and the pressure regulator valve PRV, completing the routine.As indicated at instruction block 394, the pressure command for theregulator valve PRV is set equal to the highest of the pressure commandsfor the various clutching devices.

The blocks designated by the reference numeral 388 include the decisionblock 396 for determining if a shift is in progress as indicated by the"SHIFT IN PROGRESS" flag; the decision block 398 for determining if theactual speed ratio R_(act) (that is, N_(o) /N_(t)) is equal to thedesired speed ratio R_(des) determined at instruction block 376 of FIG.13; and the instruction block 400 for setting up the initial conditionsfor a ratio shift. The instruction block 400 is only executed whendecision blocks 396 and 398 are both answered in the negative. In suchcase, instruction block 400 serves to set the old ratio variable,R_(old), equal to R_(act), to set the "SHIFT IN PROGRESS" flag, clearthe shift timers, and to calculate the fill time t_(fill) for theon-coming clutching device. If a shift is in progress, the execution ofblocks 398 and 400 is skipped, as indicated by the flow diagram line402. If no shift is in progress, and decision block 398 is answered inthe affirmative, the execution of instruction block 400 and the blocksdesignated by the reference numeral 390 is skipped, as indicated by theflow diagram line 404.

The blocks designated by the reference numeral 390 include the decisionblock 406 for determining if the shift is an upshift or a downshift; theinstruction block 408 for developing pressure commands for the active(shifting) clutching devices if the shift is an upshift; and theinstruction block 410 for developing the pressure commands for theactive clutching devices if the shift is a downshift. To illustrate howsuch pressure commands are developed, the steps involved in thedevelopment of a typical power-on upshift (i.e., instruction block 408)are set forth in the flow diagram of FIG. 15.

On entering the flow diagram of FIG. 15, the decision block 412 is firstexecuted to determine if fill phase of the shift is completed, asindicated by the "FILL COMP" flag. If not, the flow diagram branchgenerally designated by the reference numeral 414 is executed; if so,the flow diagram branch generally designated by the reference numeral416 is executed.

The flow diagram branch 414 includes a fill initializing routinecomprising the blocks 418 and 420, and a fill completion routinecomprising the blocks 422 and 424. At the beginning of each shift, the"FILL COMP" flag is not set, and the decision block 418 of the fillinitializing routine is executed to determine if the fill phase hasstarted, as indicated by the "FILL START" flag. Initially, the "FILLSTART" flag is not set, and instruction block 420 is executed to set theenergization duty cycle of the on-coming clutching device, DC(ONC),equal to 100%, to set the "FILL START" flag, and to start the FILL TIMERand the adaptive fill timer, AFILL TIMER. Thereafter, decision block418, is answered in the affirmative, and execution of instruction block420 is skipped, as indicated by the flow diagram line 426. Decisionblock 422 of the fill completion routine determines if the count in FILLTIMER is greater than or equal to the fill time t_(fill) determined atinstruction block 400 of FIG. 14. If so, instruction block 424 isexecuted to set DC(ONC) to 0%, to save the entry turbine speed N_(te),and to set the "FILL COMP" flag. If decision block 422 is answered inthe negative, the fill phase is incomplete, and execution of theinstruction block 424 is skipped, as indicated by the flow diagram line428.

The flow diagram branch 416 includes a shift initializing routinecomprising the blocks 430-436, and a shift completion routine comprisingthe blocks 438-444. Decision block 430 of the initializing routinedetermines if the "FILL COMP" flag has just been set, as indicated bythe status of the "FIRST FILL" flag. If so, the instruction blocks 432and 434 are executed to set up the torque and inertia phases of theshift. Instruction block 432 determines the pressure parameters P_(i),P_(f), and t_(f) for the on-coming (ONC) and off-going (OFG) clutchingdevices. Instruction block 434 calculates the reference inertia phaseinterval t_(rip) as a function of N_(te), R_(old), and R_(des), startsthe timer, IP TIMER, and resets the "FIRST FILL" flag. Thereafter, thedecision block 430 is answered in the negative, and the instructionblock 436 is executed to calculate the value of the term %RATCOMP foruse in the adaptive pressure correction algorithm. In the inertia phasecompletion routine, the decision blocks 438 and 440 are executed todetermine if the count in IP TIMER is at a maximum value, MAX, or if theterm %RATCOMP is substantially equal to 100%. If either of the decisionblocks 438 or 440 are answered in the affirmative, the shift is completeand instruction block 442 is executed to reset the "SHIFT IN PROGRESS"flag, to set the on-coming duty cycle, DC(ONC), equal to 100%, and toset the off-going duty cycle, DC(OFG), equal to 0%. If both decisionblocks 438 and 440 are answered in the negative, the instruction block444 is executed to determine the on-coming and off-going pressurecommands, P(ONC) and P(OFG), as a function of the P_(i), P_(f), t_(f),and IP TIMER values.

The flow diagram of FIGS. 16a-16c represents an algorithm for adaptivelycorrecting the determination of fill time t_(fill) according to thisinvention. As set forth above in reference to FIGS. 7-10, such algorithminvolves the detection of turbine speed turndown in the course of anupshift, the determination of the error E_(ft) between measured anddesired inertia phase delays, IPDELAY and DESDELAY, and the applicationof an error dependent correction amount C_(ft) to the endpoints L and Hof the stored t_(fill) vs. ΔP relationship. Generally, the portions ofthe flow diagram depicted in FIGS. 16a-16b relate to turndown detection,and the determination of error E_(ft), and the portion depicted in FIG.16c relates to the application of the correction amount C_(ft) to theendpoints L and H. The flow diagram portions are joined where indicatedby the circled numerals 1, 2, and 3.

Referring now more particularly to FIG. 16a, the decision blocks 450-452refer to initial conditions which must be satisfied before enabling theturndown detection algorithm. The detection algorithm is only enabled ifa single ratio upshift is in progress (block 450), and the turndown hasnot yet been detected (as determined by a "TURNDOWN" flag at block 452).If either condition is not met, execution of the algorithm is skipped asindicated by the flow diagram return line 456.

The turbine speed turndown detection algorithm includes an initializingroutine comprising the blocks 458-462, and an end of fill (EOF)identification routine comprising the blocks 464-486. As explainedabove, the turndown detection involves determining the time betweenpulses, T/TP, of the turbine speed signal on line 274, and novel signalprocessing of the measured times. The measurement of T/TP is made with atimer, PULSE TIMER, which is reset (enabled to start counting) each timea turbine speed pulse is identified.

The initializing routine is executed only when the algorithm is firstenabled in the course of a shift, as indicated by the "FIRST ENABLED"flag. Once the first turbine pulse is identified by the decision block460, the instruction block 462 is executed to start the PULSE TIMER andto reset the "FIRST ENABLED" flag. Thereafter, decision block 458 isanswered in the negative, and the EOF identification routine is entered.

As with the initializing routine, the EOF identification routineincludes a decision block 464 for identifying turbine speed pulses, andan instruction block 466 executed each time a pulse is identified forresetting the PULSE TIMER. Prior to resetting the PULSE TIMER, however,the time per turbine pulse, T/TP, counted by the PULSE TIMER is read andstored. Thereafter, instruction block 468 is executed to compute theaverage time between turbine pulses, AT/TP; the average change in timebetween turbine pulses, A.sup.Δ T/TP; the predicted time between turbinepulses, PT/TP(k+2) and between loop, PT/TP(L); the loop error timebetween turbine pulses, ET/TP(L); and the filtered loop error timebetween turbine pulses, FET/TP(L). Instruction block 470 is thenexecuted to determine the first and second error thresholds E_(th) (1)and E_(th) (2) as a function of the calculated FET/TP(L).

Thereafter, decision block 472 is executed to determine if the shift hasprogressed to within 200 ms of the expected end of fill. If not,instruction block 474 is executed to read the AFILL TIMER, and theremainder of the routine is skipped as indicated by the flow diagramline 488. If decision block 472 is answered in the affirmative, thedecision blocks 476 and/or 478 are executed to compare the error timeET/TP(L) to the thresholds E_(th) (1) and E_(th) (2) for determining ifa turndown has occurred. If the error time ET/TP(L) does not exceed thefirst threshold E_(th) (1), the instruction block 474 is executed toread the AFILL TIMER, and the remainder of the routine is skipped asindicated by the flow diagram return line 488. If the time error doesexceed the first threshold, the decision block 478 is executed tocompare the error time to the second threshold E_(th) (2). If the secondthreshold is exceeded, the turndown detection is assumed valid, and theinstruction block 480 is executed to set the "TURNDOWN" flag. If thesecond threshold is not exceeded, the remainder of the routine isskipped as indicated by the flow diagram line 488.

Once the turbine speed turndown has been detected, the decision block484 is executed to determine if the shift is suitable for formulation ofan adaptive correction. Examples of the indicia used to make suchdetermination include stable throttle position, positive calculatedinput torque T_(i), and suitable transmission fluid temperature. If thevarious parameters are not indicative of a normal pattern shift, theremainder of the algorithm is skipped as indicated by the flow diagramreturn line 488. If the parameters are indicative of a normal patternshift, the instruction block 486 is executed to determine the measuredinertia phase delay, IPDELAY, the desired inertia phase delay, DESDELAY,and the fill time error, E_(ft). As indicated at instruction block 486,IPDELAY is computed according to the difference between the count inAFILL TIMER and the scheduled t_(fill) ; DESDELAY is determined as afunction of the line pressure command PL and the shift type; and E_(ft)is computed according to the difference (IPDELAY-DESDELAY). As describedabove, the sign of the fill time error E_(ft) indicates whether theon-coming clutching device was overfilled (negative) or underfilled(positive), and the magnitude indicates amount of error.

To lessen the likelihood of making an erroneous fill time correction dueto spurious error, and to prevent unnecessary correction of the filltime due to a pressure scheduling error, the adaptive fill algorithmincludes a limiting routine comprising the blocks 490-512.

The blocks 490-498 operate to limit fill time corrections in response tounusually high overfill error by comparing the error term E_(ft) to anegative reference, -REF, which corresponds to a severe overfillindication. In the event of a severe overfill indication, the errorE_(ft) is limited to a relatively small value, -E_(sm), until three ormore of such error indications are determined in succession. A largeoverfill counter, LG OVF COUNTER, is used to keep track of the number ofsuccessive overfill indications. When a severe overfill is indicated (assensed by decision block 490), the instruction block 492 is executed toincrement the LG OVF COUNTER; when a smaller overfill is indicated,instruction block 494 is executed to decrement the LG OVF COUNTER. Untilthe LG OVF COUNTER is incremented to three or greater (as determined bydecision block 496), the instruction block 498 is executed to limit theerror E.sub. ft to a relatively small overfill indication, -E_(sm). Whenthe LG OVF COUNTER is incremented to three or greater, the limit is nolonger effective.

The blocks 500-502 operate in response to large positive inertia phaseerror E_(ip) (explained below in reference to FIG. 17) to limit positive(underfill) fill time error E_(ft) to a reference small value, +E_(sm).As illustrated in FIG. 6, improperly low pressure scheduling in thetorque and inertia phases reduces the torque available for deceleratingthe turbine and delays the turbine speed turndown. In such case, thelate turndown detection may be misinterpreted as an underfill error bythe fill time adaptive algorithm, even if the scheduled fill time iscorrect. To prevent significant correction of the fill time in responseto such a misinterpretation, the decision block 500 compares the inertiaphase error, E_(ip), to a positive reference, +REF, indicative ofundesirably low pressure scheduling. If the error E_(ip) exceeds thereference, +REF, the instruction block 502 is executed to limit the filltime error E_(ft) to a relatively small positive value, +E_(sm). If thereference +REF is not exceeded, the sensed fill time error E_(ft) is notlimited.

The blocks 504-512 operate to limit fill time corrections when thevehicle speed is so high that overfill (bind-up) is difficult toreliably determine. Under such conditions, the normal fill timecorrection is only permitted if turbine speed flare is sensed, or thefill time error E_(ft) indicates a relatively high underfill. In allother cases, a relatively small overfill error (-E_(sm)) is assumed. Ifthe assumed overfill error is actually incorrect, underfill errors willbe detected in successive shifting, and the correction will be reversed.The block 504 compares the vehicle speed N_(v) to a reference high speedindication, REF_(HI). If N_(v) exceeds REF_(HI), the decision block 506is executed to determine if turbine speed flare has been detected. Ifso, the underfill indication is assumed to be reliable, and the errorE_(ft) is not limited. If turbine speed flare is not detected, decisionblock 508 is executed to determine if the fill time error E_(ft) ispositive and greater than a relatively high reference value, +REF. Ifso, the instruction block 510 is executed to set the fill time errorE_(ft) equal to a moderate positive amount, +E_(mod). If E_(ft) is lessthan +REF, instruction block 512 is executed to set the fill time errorE_(ft) equal to the relatively small overfill indication, -E_(sm). IfN_(v) is not in excess of REF_(HI), the execution of blocks 506-512 isskipped as indicated by the flow diagram line 514.

Following the limiting routine, the instruction blocks 516-518 areexecuted to correct the fill time endpoints L and H in relation to theerror E_(ft) and the time integral of E_(ft). The instruction block 516updates the time integral of E_(ft) and calculates a number of termsincluding the fill time correction C_(ft), the endpoint gain factorsG_(H) and G_(L), and the endpoint correction amounts C_(LEP) andC_(HEP). The instruction block 518 applies the endpoint correctionamounts C_(LEP) and C_(HEP) to the endpoints L and H, respectively. Asdescribed above in reference to FIG. 9, the correction amount C_(ft) isdetermined as a function of E_(ft) and the time integral of E_(ft). Asdescribed above in reference to FIG. 10, the gain factors G_(L) andG_(H) are determined as a function of the line pressure command PL, therespective gain factors being multiplied by the correction amount C_(ft)to determine the endpoint correction amounts C_(LEP) and C_(HEP).

The adaptive pressure correction algorithm is depicted by the flowdiagram of FIG. 17. As described above, the algorithm comprises thesteps of obtaining a measure t_(ip) of the inertia phase interval,comparing t_(ip) to a reference interval t_(rip) to obtain an inertiaphase error term E_(ip), and correcting the stored pressure endpoints inrelation to E_(ip) and the time integral of E_(ip). The measuredinterval begins when the ratio shift is 20% complete and ends when theratio shift is 80% complete, as judged by the term %RATCOMP. Thealgorithm includes an initializing routine, an interval measurementroutine, and a correction routine. The initializing routine comprisesthe blocks 520-526; the interval measurement routine comprises theblocks 528-542; and the correction routine comprises the blocks 544-546.

In the initializing routine, the decision blocks 520 and 522 areexecuted to determine if a single ratio upshift is in progress, and ifthe ratio shift is at least 20% complete, as judged by the term,%RATCOMP. If either of the decision blocks 520 and 522 are answered inthe negative, the remainder of the flow diagram is skipped, as indicatedby the flow diagram return line 550. When both are answered in theaffirmative, the decision block 524 is executed to determine if the IPflag is set. This flag marks the beginning of the measured inertia phaseinterval, and is set by the instruction block 526 the first time thatdecision block 524 is executed. Instruction block 526 also serves tostart the IP TIMER. Thereafter, instruction block 524 is answered in thenegative, and the measurement routine is entered.

In the measurement routine, the decision block 528 is executed tocompare the count in the IP TIMER with the reference interval, t_(rip).So long as the count in IP TIMER is less than t_(rip), the blocks530-534 are executed to stop IP TIMER at 80% completion and to calculatethe inertia phase error E_(ip) according to the difference (IPTIMER-t_(rip)). However, when the count in IP TIMER exceeds t_(rip), theblocks 536-542 are executed to either (1) set the error E_(ip) at apredetermined large value, E_(LG), if the shift is less than 50%complete, or (2) compute the error E_(ip) in relation to the differencebetween t_(rip) and a linear extrapolation of the inertia phase time,t_(ip). In the later case, the time t_(ip) is extrapolated from thecurrent values of IP TIMER and %RATCOMP, as indicated at instructionblock 540 by the expression:

    t.sub.ip=(IPTIMER*. 60)/(%RATCOMP-.20)

Once the inertia phase error E_(ip) is determined, the decision block542 is executed to determine if the various parameters monitored in thecourse of the shift are indicative of a normal pattern shift. Asdescribed above in reference to the adaptive fill time correction, suchparameters include stable throttle position, positive torque, andsatisfactory oil temperature throughout the shift. If decision block 542is answered in the affirmative, an adaptive pressure correction may bereliably made and the correction routine is entered.

In the correction routine, the instruction blocks 544 and 546 areexecuted to correct the pressure endpoints P_(a), P_(b), P_(c), andP_(d) in relation to the error E_(ip) and the time integral of E_(ip).The instruction block 544 updates the time integral of E_(ip) andcalculates a number of terms including the inertia phase pressurecorrection C_(ip), the endpoint gain factors G_(H) and G_(L), and theendpoint correction amounts C_(LEP) and C_(HEP). Instruction block 546applies the endpoint correction amounts C_(LEP) and C_(HEP) to thepressure endpoints. As described above in reference to FIG. 9, thecorrection amount C_(ip) is determined as a function of E_(ip) and thetime integral of E_(ip). As described above in reference to FIG. 10, thegain factors G_(L) and G_(H) are determined as a function of the torquevariable T_(v), the respective gain factors being multiplied by thecorrection amount C_(ip) to determine the endpoint correction amountsC_(LEP) and C_(HEP). The endpoint correction amount C_(LEP) is appliedto the pressure endpoints P_(a) and P_(b), while the endpoint correctionamount C_(HEP) is applied to the pressure endpoints P_(c) and P_(d). Infuture shifts, the pressure supplied to the subject clutching devicewill result in an inertia phase interval more nearly equal to thereference interval t_(rip), and a more nearly optimum quality shift.

While this invention has been described in reference to the illustratedembodiment, it will be understood that various modifications will occurto those skilled in the art, and that systems incorporating suchmodifications may fall within the scope of this invention which isdefined by the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. In a shift controlsystem for a motor vehicle multiple speed ratio automatic transmissionhaving a fluid operated torque establishing device associated with aspecified speed ratio and a source of fluid pressure, wherein shiftingfrom a currently engaged speed ratio to said specified speed ratioincludes a shift completion phase during which fluid is supplied to thetorque establishing device by an open-loop control technique inaccordance with a predetermined pressure schedule to initiate andprogressively increase the torque transmission therethrough, a method ofadaptively correcting the predetermined pressure schedule for sources oferror which affect the increase of torque transmission through thetorque establishing device during the completion phase and therebydegrade the shift quality, said method comprising the stepsof:repeatedly computing a measure of the speed ratio progression duringthe completion phase of the shift as a function of the transmissioninput and output speeds; measuring the time interval required for thecomputed measure of speed ratio progression to change from a firstpredefined value to a second predefined value, and comparing suchmeasured time interval to a reference time interval representative ofthe time that would be required to effect such change when the shiftquality is not degraded; and adjusting the predetermined pressureschedule in relation to the deviation between the measured and referencetime intervals such that the scheduled pressure in subsequent shifts tothe specified speed ratio is increased if the measured time interval issignificantly longer than the reference time interval and decreased ifthe measured time interval is significantly shorter than the referencetime interval, thereby to improve the shift quality in such subsequentshifts.
 2. The method set forth in claim 1, wherein the first and secondpredefined values represent a portion of the speed ratio progressionwhich is substantially linear with respect to time.
 3. The method setforth in claim 1, including the step of:determining the amount ofadjustment of said predetermined pressure schedule in accordance with afirst term dependent on the difference between said measured andreference time intervals and a second term dependent on the integral ofsuch difference with respect to time.
 4. The method set forth in claim3, including the step of:resetting said second term to zero when thedifference between said measured and reference time intervals changessign and has a magnitude in excess of a reference amount.
 5. The methodset forth in claim 3, including the step of:limiting the amount ofadjustment of said predetermined pressure schedule to a maximumreference determined in relation to the difference between said measuredand reference time intervals.
 6. In a shift control system for a motorvehicle multiple speed ratio automatic transmission having a fluidoperated torque establishing device associated with a specified speedratio and a source of fluid pressure, wherein shifting from a currentlyengaged speed ratio to said specified speed ratio includes a shiftcompletion phase during which fluid is supplied to the torqueestablishing device by an open-loop control technique in accordance witha predetermined pressure schedule to inititate and progressivelyincrease the torque transmission therethrough, a method of adaptivelycorrecting the predetermined pressure schedule for sources of errorwhich affect the increase of torque transmission through the torqueestablishing device during the completion phase and thereby degrade theshift quality, said method comprising the steps of: p1 repeatedlycomputing a measure of the speed ratio completion as a function of thetransmission input and output speeds;establishing first and secondreference values which define a selected portion of the ratio shiftprogression; initiating an elapsed time measurement when the measure ofspeed ratio completion reaches the first reference value and terminatingthe elapsed time measurement when the measure of speed ratio completionreaches the second reference value; developing a time error term inrelation to the difference between the elapsed time meansurement and areference time interval representative of the time that would berequired to effect such change when the shift quality is not degraded;and adjusting the predetermined pressure schedule in relation to thetime error term such that the scheduled pressure in subsequent shifts tothe specified speed ratio is increased if the elapsed time measurementis significantly longer than the reference time interval and decreasedif the elapsed time measurement is significantly shorter than thereference time interval, thereby to improve the shift quality in suchsubsquent shifts.
 7. The method set forth in claim 6, including the stepof:identifying the point at which the elapsed time measurement reachesthe reference time interval; and thereafter setting the time error termto a predetermined high value if the measure of speed ratio completionis less than a third reference value intermediate said first and secondreference values.
 8. The method set forth in claim 6, including the stepof:identifying the point at which the elapsed time measurement reachesthe reference time interval; and thereafter predicting a future value ofthe elapsed time measurement as a function of the current value of theelapsed time measurement and the current measure of speed ratio shiftprogression if the measure of speed ratio shift progression is greaterthan a third reference value intermediate said first and secondreference values.